How to Install MacOS Sierra 10.12 Beta Safely & Dual Boot El Capitan

Creating a dual boot environment is an ideal solution for Mac users who want to install and try macOS Sierra but without interfering with their primary stable Mac OS X El Capitan installation. This tutorial will walk through the entire process of setting up such an environment, including partition a disk, and installing macOS Sierra 10.12 beta onto that partition to allow for a dual boot.

The process of creating a dual boot Mac OS environment is not particularly difficult but it involves some risk and setup steps which could result in catastrophic data loss, thus this is generally aimed at advanced users and is not appropriate for novices. Completing a full system backup beforehand is essential.

While we’re focusing on installing MacOS Sierra onto a partition for dual boot purposes, you can also install macOS Sierra onto an external hard drive, a USB drive, or even an SD card, and have the same dual boot situation between the macOS Sierra beta and the OS X El Capitan stable release, though performance is usually not as good when an operating system is running off an external volume.

Sufficient hard disk space on the Mac to allow for a new partition to be created to run MacOS Sierra from (assume 20GB or more for Sierra partition, and allow at least 10GB of storage on the primary Mac OS X installation as well)

If it is a Mac laptop, connect to a power source before beginning

Be sure you have backed up your Mac before beginning this process. You will be partitioning a hard drive and then installing beta system software. Failure to adequately backup your Mac and your data may result in permanent data loss, do not skip a backup.

How to Create a MacOS Sierra Partition

You will need to partition the hard drive of the Mac to add a new partition for which to install Mac OS Sierra onto. This allows MacOS Sierra to run in a self-contained installation without impacting your primary stable OS X EL Capitan installation, thus allowing the dual boot. Here’s how to add a partition:

Open Disk Utility, the app is found in /Applications/Utilities/

Choose your hard drive from the left menu list

Click the “Partition” button, then click the [+] plus button to create a new partition

Name the new partition something very obvious like “Sierra”, and then assign the partition a reasonable amount of space (20GB minimum or more is a good idea for basic testing)

Choose “Apply” to finish and to create the new partition on the drive

Quit out of Disk Utility when finished, you’re now ready to install MacOS Sierra on the new partition.

How to Install MacOS Sierra to the New Partition

Assuming you backed up, partitioned the Mac, and have macOS Sierra downloaded, you can now safely install MacOS Sierra 10.12 onto the separate partition, this will allow you to preserve your existing OS X installation without potentially messing it up with the new beta system software.

Launch the MacOS Sierra Installer from the /Applications/ folder on the Mac, it is currently labeled as “Install 10.12 Developer Preview.app”

Go through the installer as usual, when you get to the disk selection screen, choose “Show All Disks” and choose “Sierra” from the list, then click on “Install” to begin installing MacOS Sierra onto that partition

Let the installation run its course, the Mac will reboot to complete the job, and when finished the computer will automatically boot into macOS Sierra when installation is complete

Now you’re in macOS Sierra running off the separate partition, this gives you access to files on your Mac but preserves the other stable operating system, in this case OS X El Capita. For what it’s worth, this would work the same with OS X Yosemite and Mavericks too if you’re wanting to dual boot Sierra with those releases as well.

You can now easily dual boot between MacOS Sierra and the other stable Mac OS X release. This is quite simple, if you want to switch between the operating systems, all you do is:

Reboot the Mac from the  Apple menu as usual

Hold down the OPTION key when you hear the boot chime sound

Select the drive and operating system you want to boot from and use, whether MacOS Sierra or OS X El Capitan

It’s that simple, you can reboot and switch between the operating systems running on the same Mac with ease.

Removing the MacOS Sierra Beta Partition

If you ever want to get rid of one of the operating systems, or remove the MacOS Sierra beta partition, just go back into Disk Utility and delete the partition you wish to remove. Keep in mind that if you delete a partition, you not only lose the operating system on that partition, but you also delete all data and files on that partition. Always backup, and be smart.

You could use a symlink for that, but a better solution would be to install Drop Box in macOS Sierra as well as your primary OS X installation. Then you can access and use files from DropBox via either OS install without having to access the other file system. Regardless you’d be able to mount and access the other OS drive, but considering it’s a beta OS it’s best to leave the primary OS alone and entirely separate from the beta in my experience.

But remember that Sierra is not ready for primetime, it would be wise for most to wait for a public release.

I just want to be clear regarding your definition of “DUAL BOOT”. To me, dual boot means both operating systems RUNNING at the same time, side by side. Is this what you are referring to, or are you confusing dual boot with multiple boot drives? (although the two boots are on the same drive) If you do actually mean two OS versions running at the same time, side by side, can it be done with two internal hard drives?

I was wondering if this is safe to do with a mac already running Windows 7 on a partition using BootCamp or will it wipe the partition table making the above changes?

El Capitan is running well and I’ve got TONS of space for the Beta but not if I’m going to have to spend hours getting my Capitan or Windows back like I did when I stupidly used TechTool Pro 7 to set up a recovery partition.

I have a lot of confidence in the mac software team but for some reason it seems the BootCamp camp is dwindling.

I have mountian lion running still on my late 2010 macbook pro. I want to do a dual install of Sierra and wonder if that will work. I have older software that I really need on my mac, so I don’t want to upgrade higher than mountain lion in fear of losing it. What is your advice? (thank you in advance)

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